Brick Pressing Rate Calculations

Introduction

Under the assumption of incompressible flow and fixed hydrauilic cylinder volume, the brick pressing rate of The Liberator can be calculated for a given hydraulic flow rate.

The Liberator

The Liberator uses a 5x8x2 inch cylinder (diameter x length x rod diameter) for pressing, and a 2.5x14x1.125" cylinder for the soil loading drawer.

The effective volumes for both cylinders differ. This is because the cylinder rod takes up some volume - thereby reducing effective volume and force for the contraction part of the stroke. The expansion part of the stroke uses the full cylinder volume.

Main Cylinder Volume, D= 5 inches, D_rod=2 inches

• Cylinder volume (expansion volume) = 157 cu in
• Rod volume = 25 cu in
• Cylinder volume-rod volume (contraction volume) = 132 cu in
• Volume filled for a complete cycle of the cylinder (expansion volume + contraction volume) = 289 cu in

Secondary Cylinder Volume, d=2.5 inches, d_rod=1.125 inches

• Cylinder volume (expansion volume) = 69 cu in
• Rod volume = 14 cu in
• Cylinder volume-rod volume (contraction volume) = 55 cu in
• Volume filled for a complete cycle of the cylinder (expansion volume + contraction volume) = 124 cu in

One complete cycle volume

One cycle volume = 413 cu in

1 gallon = 231 cu in

1 cycle = 1.8 gallons of fluid

Assuming 24 gallons per minute are available, this translates to 13 bricks per minute. Assume that compression requires 10% extra time because of operation under compression load for a small part of the pressing cycle - and you have 12 bricks per minute for full, 4.25" thick bricks.

Assume that for example 3" tall bricks are desired. These can be produced with 6 inches of main cylinder motion, or 3/4 of the full cycle volume, or 216 cu in. The cycle total is thus 341 cu in, or 1 cycle = 1.5 gallons. This constitutes 16 bricks per minute. Asume 10% extra time as above, and the final result is 14 bricks per minute.